Chemical mechanical planarization (CMP) is used extensively in the manufacture of semiconductor chips and memory devices. During a CMP process, material is removed from a wafer substrate by the action of a polishing pad, a polishing slurry, and optionally chemical reagents. Over time, the polishing pad becomes matted and filled with debris from the CMP process. Periodically the polishing pad is reconditioned using a pad conditioner that abrades the polishing pad surface and opens pores and creates asperities on the surfaces of the polishing pad. The function of the pad conditioner is to maintain the removal rate in the CMP process.
CMP represents a major production cost in the manufacture of semiconductor and memory devices. These CMP costs include those associated with polishing pads, polishing slurries, pad conditioning disks and a variety of CMP parts that become worn during the planarizing and polishing operations. Additional cost for the CMP process includes tool downtime in order to replace the polishing pad and the cost of the test wafers to recalibrate the CMP polishing pad.
A typical polishing pad comprises closed-cell polyurethane foam approximately 0.16 centimeters thick. During pad conditioning, the pads are subjected to mechanical abrasion in order to physically cut through the cellular layers of the pad surface. The exposed surface of the pad contains open cells, which can be used during the CMP process to trap abrasive slurry consisting of the spent polishing slurry and material removed from the wafer. In each subsequent pad-conditioning step, the pad conditioner removes the outer layer of cells containing the embedded materials and minimizes removal of layers below the outer layer. Over-texturing of the polishing pad results in a shortened life, while under-texturing results in insufficient material removal rate and lack of wafer uniformity during the CMP step.
One type of CMP pad conditioner is a four-inch disc with fixed diamond abrasives. The diamond coated disc is rotated and pressed onto the polishing pad surface to cut and remove the top layer. The diamonds are typically set in an epoxy or a metal matrix material. However diamonds from these pad conditioners can become dislodged which can lead to yield loss due to scratching of the wafer during the polishing operation.
There is a continuing need for CMP pad dressers that reduce or eliminate abrasive particles becoming dislodged and CMP pad dressers that have varying surface heights for dressing CMP polishing pads.